Lab 5.3.3 Rollover Cable

Estimated time: 30 min.

Objectives:

  • Build a rollover cable for connection from a workstation to the console port on a router or switch

Background:

In this lab you learn how to build a Category 5 (CAT 5) Unshielded Twisted Pair (UTP) console rollover cable and test it for good connections (continuity) and correct pinouts (correct wire on the right pin). This will be a 4-pair (8-wires) "rollover" cable.

This cable should be approximately 10 feet in length but can be as long as 25 feet. It can be used to connect a workstation or dumb terminal to the console port on the back of a router or Ethernet switch in order to be able to configure the router or switch. This cable uses an asynchronous serial interface to the router or switch (8 data bits, No parity and 2 Stop bits). Both ends of the cable you build will have RJ-45 connectors on them. One end plugs directly into the RJ-45 console management port on the back of the router or switch and the other end plugs into an RJ-45-to-DB9 terminal adapter. This adapter converts the RJ 45 to a 9-pin female D connector that plugs into the DB9 serial port male adapter on the back of a PC running terminal emulation software such as HyperTerminal. A DB25 terminal adapter is also available to connect with a dumb terminal which has a 25 pin connector.

A rollover cable uses 8 pins but is different from the straight-through cable or crossover cable that you will build in other labs. With a rollover cable, pin 1 on one end connects to pin 8 on the other end. Pin 2 connects to pin 7, pin 3 connects to pin 6 and so on. This is why it is referred to as a rollover since the pins on one end are all reversed on the other end as though one end of the cable was just rotated or rolled over.

A flat black rollover cable comes with each new router or switch along with the terminal adapters for both DB9 and DB25 connections to terminals or PC serial ports. It is approximately 8 feet long. This lab will enable you to build another cable if the one that comes with the router or switch is damaged or lost. It will also allow you to connect to routers or switches from workstations that are greater than 8 feet away by building your own longer cables.

Tools / Preparation:

Prior to starting the lab, the teacher or lab assistant should have a spool of Cat 5 Unshielded Twisted Pair (UTP) cable, RJ-45 (8-pin) connectors, an RJ-45 crimping tool and a continuity tester available. Work individually or in teams.  The following resources will be required:

  • 10 to 20 foot length of Cat 5 cabling (one per person or one per team)
  • Four RJ-45 connectors (two extra for spares)
  • RJ-45 crimping tools to attach the RJ-45 connectors to the cable end
  • An RJ-45 to DB9 female terminal adapter (available from Cisco)
  • Cabling continuity tester
  • Wire cutters


Step 1. Review Cable Connections and Pin Locations

Use the table as a reference to answer the questions below and to help you create a rollover console cable.

Questions:
  1. Which signal on the Router port (column 1 of the table) will be used to transmit data to the PC when the PC is first connected and HyperTerminal is started (this is what displays the router prompt on the workstation.)?

     
  2. Which pin is this connected to on the router end of the RJ-45 cable? __________________
  3. Which pin is this connected to on the other end of the RJ-45 cable? ___________________
  4. Which pin is this connected to in the DB9 connector? ______________________________
  5. Which console device signal does this connect to? ________________________________
  6. What would happen if pin 3 on the left cable end were attached to pin 3 as with a straight-thru cable?



Rollover Console Cable Table

For connecting from a router or switch console port to a PC workstation running HyperTerminal terminal emulation software. Console port signaling and cabling using an RJ-45 rollover and DB9 Adapter.

Router or switch Console port (DTE) RJ-45 to RJ-45 Rollover Cable (left end)  RJ-45 to RJ-45 Rollover Cable (right end) RJ-45 to DB9 Adapter Console Device (PC workstation serial port)
Signal  From RJ-45 Pin No. To RJ-45 Pin No. DB9 Pin No. Signal
RTS 1 8 8 CTS
DTR 2 7 6 DSR
TxD 3 6 2 RxD
GND  4 5 5 GND
GND 5 4 5 GND
RxD 6 3 3 TxD
DSR  7 2 4 DTR
CTS  8 1 7 RTS

Signal Legend: RTS = Request To Send, DTR = Data Terminal Ready, TxD = Transmit Data, GND = Ground (One for TxD and one for RxD), RxD = Receive Data, DSR = Data Set Ready, CTS = Clear To Send.


 Step 2. Use the following steps to build the rollover console cable.
  1. Determine the distance between devices, then add at least 12" to it. Make your cable about 10 feet unless you are connecting to router or switch from a greater distance. The maximum length for this cable is about 8m (appx 25 feet).
  2. Strip 2" of jacket off of one end of the cable.
  3. Hold the 4 pairs of twisted cables tightly where jacket was cut away, then reorganize the cable pairs and wires into the order of the 568-B wiring standard. You can order them in any sequence but use the 568-B sequence to become more familiar with it.
  4. Flatten, straighten, and line up the wires, then trim them in a straight line to within 1/2" - 3/4" from the edge of the jacket. Be sure not to let go of the jacket and the wires, which are now in order!
  5. Place an RJ-45 plug on the end of the cable, with the prong on the underside and the orange pair to the left side of the connector.
  6. Gently push the plug onto wires until you can see the copper ends of the wires through the end of the plug. Make sure the end of the jacket is inside the plug and all wires are in the correct order. If the jacket is not inside the plug, it will not be properly strain relieved and will eventually cause problems. If everything is correct, crimp the plug hard enough to force the contacts through the insulation on the wires, thus completing the conducting path.
  7. Repeat steps 2-6 to terminate the other end of the cable, but reversing every pair of wires as indicated in the table above. (pin 1 to pin 8, pin 2 to pin 7, pin 3 to pin 6 and so on. Alternate Method - Arrange the wires into the order of the 568-B wiring standard. Place a RJ-45 plug on the end with the prong on the top side of the connector. This method will achieve the proper reversing of every pair of wires.
  8. Test the finished cable and have the instructor check it. How can you tell if your cable is functioning properly?

LAB 5.3.3 – ROLLOVER CABLE - ANSWERS

Step 1

Review Cable Connections and Pin Locations

Use the table as a reference to answer the questions below and to help you create a rollover console cable.

Questions:

1. Which signal on the Router port (column 1 of the table) will be used to transmit data (showing the router prompt etc.) to the PC when the PC is first connected and HyperTerminal is started? TxD

2. Which Pin is this connected to on the router end of the RJ-45 cable? 3

3. Which pin is this connected to on the other end of the RJ-45 cable? 6

4. Which pin is this connected to in the DB9 connector? 2

5. Which console device signal does this connect to? RxD

6. What would happen if Pin 3 on the left cable end were attached to pin 3 as with a straight-thru cable? (Transmit Data (TxD) from the router would be connected to the Transmit Data (TxD) on the workstation and they would never communicate.


Step 2

Use the following steps to build the rollover console cable.

8. Test the finished cable and have the instructor check it. How can you tell if your cable is functioning properly? There are several methods that can be used to check the cable.

Visual Test: The cable ends can be visually inspected and should be wired exactly opposite when looking at the conductors and holding the RJ-45 connectors side by side with the clip facing down. If you hold the RJ-45 connectors end to end with the clip facing down the wire colors should match. Pinouts are listed in the table.

Cable Test: You can test the cable with a cable tester to verify the wires have continuity (no breaks) and are not shorted.

Functional Test: You can connect your rollover cable to the RJ-45-to-DB9 terminal adapter and connect a workstation to the router to verify that you can see the router console prompts. This is the ultimate test and also requires that HyperTerminal be set up properly on the Workstation (8 data bits, No parity, 2 Stop bits)